Generally, the tape reel for the video cassette tape comprises a hub for winding a magnetic tape into a roll thereon and two flanges attached one each to the opposite axial ends of the hub, and it is made of a plastic material. The hub possesses a blind engaging hole bored inwardly from one axial end thereof, provided on the inner wall surface thereof with a plurality of ribs and adapted for engagement with the reel engaging shaft on the cassette recording/playback machine. The hub is further provided at the center on the other axial end thereof with a small protuberance adapted for contact with the resilient retainer piece on the cassette case side.
In the tape reel of the construction described above, one of the flanges is integrally molded at one axial end of the hub, while the other flange is independently molded and subsequently joined to the remaining free axial end of the hub by means of ultrasonic welding. Otherwise, the joining is accomplished by separately forming the aforementioned small protuberance with a different material and providing the carrier member of the small protuberance with engaging means.
While the independently molded flange is being joined by ultrasonic welding to the aforementioned free axial end of the hub, either one or both of these components tend to sustain cracks and fractures. Even after the flange has been joined to the hub, either component may sustain distortion. Occurrence of such faults has been frequently experienced by the conventional tape reel. The inventor's study in search of causes for such phenomena has revealed that the ultrasonic waves used during the work of fastening the independently molded flange to the hub produce more vibratory force than would be reasonably expected and, because of the resultant resonance, inflict cracks and fractures upon the hub and/or the flange and even cause the flange to be fastened to the hub in a distorted state.